1. Field of the Invention
The present invention relates to a system and method for automatically determining gas-liquid relative permeability of liquid saturated core samples.
2. Discussion of the Background of the Invention:
One important consideration in evaluating reservoir characteristics of oil fields relates to a determination of the gas-liquid relative permeability of core samples from such reservoirs. Determination of such permeability figures are important in those oil fields producing by gas cap expansion, gravity drainage, solution gas, or injected gas drive.
Jones and Roszelle in "Graphical Techniques for Determining Relative Permeability From Displacement Experiments", May, 1978, Journal of Petroleum Technology, set forth various graphical techniques for rapidly and yet accurately determining gas/liquid relative permeability. A discussion of the apparatuses necessary for producing raw data are conventional and are, for example, discussed in "Lefebvre DU Prey, E."; "Mesure Des Permeabilities Relatives Par La Methode De Welge", September-October, 1973; Revue De L'Institut Francais DU Petrole, pages 695-715 and in Owens, et al. "An Evaluation of a Gas Drive Method For Determining Relative Permeability Relationships", Petroleum Transactions (AIME), Volume 207, 1956, pages 275-280. In the Owens article, the author recognizes that a primary goal in oil production research laboratories is the design of a simple and inexpensive, yet reliable approach for measuring the gas-oil flow characteristics of reservoir rock samples. The article classifies experimental methods into the three classifications of steady state, stationary liquid method, and non-steady state method.
The present invention pertains to the non-steady state method wherein a gas such as helium is injected into the core sample causing displacement of the liquid within the core sample thereby resulting in a system of continually changing average saturation and saturation gradient. The non steady state method is also termed, by Owens, the "gas drive method." Owens sets forth an apparatus and procedure for performing the gas drive relative permeability measurements. Owens discloses a means for separating and measuring the produced oil and gas volumes wherein the oil is captured in an oil burette and the gas is captured in a gas burette.
The approach set forth by Owens and others for measuring gas-liquid relative permeability under the gas drive method is a lengthy process requiring constant monitoring. The produced liquid is manually read from a burrette as set forth in the Owens reference or from a series of collection bottles.